Sahih Muslim Book 6, Hadith Number 2500.

Chapter : Fasting on the day of ‘Ashura (1Oth of Muharram).

This Hadith is narrated on the authority of Hisham with the same chain of transmitters, but he made no mention in the first part of the Hadith that the Messenger of Allah (may peace be upon him) used to observe fast, and said about the second part that he abandoned the (fast) of Ashura, and he who wished observed the fast and who wished otherwise abandoned it, and he did not hold it as the words of the Apostle of Allah (may peace be upon him) as mentioned in the narration transmitted by Jarir.